1. Field of the Invention
This invention relates to a heat-insulating engine with swirl chamber equipped with nozzles for effecting main injection and subsidiary injection into swirl chambers.
2. Description of the Prior Art
It is known conventionally that when a pre-mixture is sucked to a certain extent and the sucked pre-mixture is compressed and then injected from nozzles in a Diesel engine, the engine output can be improved and the occurrence of smoke and the like can be reduced. In this case, since the pre-mixture has an extremely lean mixture ratio and is distributed substantially uniformly throughout the cylinders, the pre-mixture existing near the cylinder walls and in the gap between the top land of a piston head an cylinder liners is not burnt even after the fuel is injected from ordinary nozzles and is exhausted as an unburnt gas and thus results in deterioration of hydrocarbon components of the fuel.
The structure of a heat-insulating engine utilizing a ceramic material as a heat-insulating material or as a heat-resistant material is conventionally disclosed, for example, in Japanese Patent Application No. 180250/1988 (Japanese Patent Laid-Open No. 33454/1000). The structure of the heat-insulating piston described in this prior art reference is such that a main combustion chamber made of a high density ceramic thin sheet and fitted to a cylinder head through a heat-insulating material communicates with swirl chambers whose swirl chamber blocks are made of a material having low heat conductivity and have their inner wall surfaces composed of a high density ceramic thin sheet and which are provided with fuel injection nozzles. In the structure of this heat-insulating engine, the main combustion chamber has a unitary structure of a head lower surface thin sheet made of a high density ceramic and opposing the lower surface of the cylinder head and a liner thin sheet, the liner thin sheet is fitted to the upper portion of a cylinder liner made of a material having low heat conductivity, inlet/outlet passage of the swirl chambers communicate with the openings formed on the head lower surface thin sheet and the portion of the piston head on the main combustion side is composed of the head thin sheet made of a high density ceramic.
In the structure of the heat-insulating engine disclosed in Japanese Patent Application No. 180250/1988 described above, the thermal capacity of the ceramic members constituting the wall surfaces of the main combustion chamber and swirl chambers is reduced as much as possible to improve suction efficiency of the engine, mixing between atomized fuel and air is promoted rapidly by the improvement in suction efficiency and the fuel equivalent ratio is reduced drastically in order to reduce the combustion time in a smoke generation temperature zone and to avoid the combustion in a NOx generation temperature zone. Moreover, the structure can prevent the decrease of strength resulting from the reduction of thickness of the ceramic material.
In the heat-insulating engine such as the one described above, there remains the problem as to how the heat-insulating engine with swirl chamber be constituted in order to further recover the heat energy from the inner wall of the swirl chambers, to prevent the lean mixture from diffusing into the cylinders and thus to eliminate deterioration of the hydrocarbons of the fuel.